1. Field of Invention
The embodiments of the invention generally relate to a method and apparatus for transferring substrates in a semiconductor processing system.
2. Background of Invention
Semiconductor substrate processing is typically performed by subjecting a substrate to a plurality of sequential processes to create devices, conductors and insulators on the substrate. These processes are generally performed in a process chamber configured to perform a single step of the production process. In order to efficiently complete the entire sequence of processing steps, a number of process chambers are typically coupled to a central transfer chamber that houses a robot to facilitate transfer of the substrate between the surrounding process chambers. A semiconductor processing platform having this configuration is generally known as a cluster tool, examples of which are the families of PRODUCER®, CENTURA® and ENDURA® processing platforms available from Applied Materials, Inc., of Santa Clara, Calif.
Generally, a cluster tool consists of a central transfer chamber having a robot disposed therein. The transfer chamber is generally surrounded by one or more process chambers. The process chambers are generally utilized to sequentially process the substrate, for example, by performing various processing steps such as etching, physical vapor deposition, chemical vapor deposition, ion implantation, lithography and the like. As the processes performed in the process chambers are generally performed at vacuum pressure, the transfer chamber is maintained at vacuum pressure as well to eliminate having to repeatedly pump down the process chamber for each substrate transfer. This is partially important as pumping down the transfer chamber may require as much as eight hours to reach operational vacuum levels.
Load lock chambers are generally used to facilitate transfer of the substrates between the vacuum environment of the transfer chamber and an environment of a factory interface wherein substrates are stored in cassettes. The factory interface is typically at or near atmospheric pressure. The load lock chambers are selectively isolated from the factory interface and transfer chamber by slit valves. Generally, at least one slit valve is maintained in a closed position to prevent loss of vacuum in the transfer chamber during substrate transfer through the load lock. For example, an interface slit valve is opened while a chamber slit valve is closed to allow an interface robot to transfer substrates between the load lock chamber and the substrate storage cassettes disposed in the factory interface. After the substrate is loaded from the interface robot, both slit valves are closed as the load lock chamber is evacuated by a pump to a vacuum level substantially equal to that of the transfer chamber. The substrate in the evacuated load lock is passed into the transfer chamber by opening the chamber slit valve while the interface slit valve remains closed. Processed substrates are returned to the factory interface in the reverse manner, wherein the load lock chamber is vented to substantially equalize the pressure between the load lock chamber and the factory interface.
There are generally two types of load lock chambers utilized to interface with the transfer chamber. A first type is known as a batch-type load lock chamber. The batch-type chamber generally holds an entire substrate storage cassette within the chamber. The cassette is loaded into the load lock chamber and the chamber is sealed and pumped down to an appropriate vacuum level. The chamber is then opened to the transfer chamber so that the robot within the transfer chamber may freely access any of the substrates and storage slots within the cassette until all of the substrates within the cassette have been processed. After all the substrates have been returned to the cassette, the load lock chamber is isolated from the transfer chamber to facilitate replacing the cassette with another cassette containing substrates to be processed. While the cassettes are being exchanged, the transfer robot typically draws substrates from a cassette disposed in a second load lock chamber coupled to the transfer chamber.
The use of batch-type load lock chambers is generally a robust and effective system for transferring substrates into the transfer chamber. However, due to the relatively large internal volume required to accommodate the entire substrate cassette, pump-down times are long and the associated pumping hardware is large and costly. Additionally, venting of the large internal volume increases the chance of particulate contamination and condensation on the substrates.
The second type of load lock chamber is known as a single substrate-type. Generally, the single substrate-type load lock chamber shuttles one processed and one unprocessed substrate therethrough each time the load lock chamber is pumped down. To maintain high system throughput, single substrate-type load lock chambers are typically used in tandem. This allows a first load lock chamber to exchange substrates with the transfer chamber while a second load lock chamber exchanges substrates with the factory interface wherein the substrate storage cassettes are positioned.
Cluster tools often utilize more than one load lock to maintain high substrate transfer rates between the factory interface and the transfer chamber. However, the second load lock occupies a position on the transfer chamber at the expense of an additional process chamber throughput and process versatility is sacrificed. Thus, if one of the load lock chambers could be eliminated without loss of substrate exchange rates between the transfer chamber and factory interface, an additional process chamber could be utilized in the open facet of the transfer chamber, thus enhancing system throughput and versatility. Moreover, utilizing a single load lock chamber would advantageously reduce the cost of ownership for the system.
Therefore, there is a need for an improved load lock chamber.